You can do it with a standard toilet plunger, no inner flange. I have a perko now, however it can be done. I used the plunger, had my old rabbit ears from my I/O - removed the hose connection from that, cut a hole in the side of the plunger, stuck it through, silicone it in.
Trick is to have the hose portion pointed directly at the scupper. Plenty of water for about a 15 minute engine run before temp started to rise.